1. Field of the Invention
The present invention relates to a touch screen system, and relates more particularly to an optical touch screen system that can detect movement perpendicular to a touch screen.
2. Description of the Related Art
A touch screen system generally includes a touch screen, and input operations are performed by contacting the touch screen with an object or a pointer. After the touch screen system detects the contact of the pointer with the touch screen, the position of the contact is calculated and coordinates are outputted for next operating procedure. There are various methods for detecting the contact of a pointer, one of which uses an optical imaging touch screen technology that detects the blocking of light for tracing the movement of a pointer on a touch screen.
An optical touch screen system using the optical imaging touch screen technology may include a touch screen, multiple image sensors disposed adjacent to the touch screen, and a plurality of reflecting components disposed on the sides of the touch screen. An object on the touch screen blocks a portion of light so that dark areas are formed on the image sensors. The coordinates of the object can be computed using the dark areas on the image sensors.
The optical detecting assembly including the image sensors and reflecting components (or active light emitting devices) has a definite thickness. Before an object approaching the touch screen contacts the touch screen, a dark area is formed on the image sensor and the optical touch screen system starts to calculate the coordinates of the object in response to the generation of the dark area. However, a significant difference always exists between the coordinates of the object calculated before the object contacts the touch screen and the coordinates of the object calculated after the object contacts the touch screen. Similarly, when the object is moved away from the touch screen, a significant difference exists between the coordinates of the object calculated before the object is moved from the touch screen and the coordinates of the object calculated after the object leaves the touch screen. Continuous output of erroneous coordinates may cause motion blur effect.
In addition, although current optical touch screen systems can accurately calculate the position of an object, they cannot detect the amount of force applied on the touch screen by the object. Thus, the application of the current optical touch screen systems is limited.